This invention relates to a device for and a method of inspecting the surface of a target object having a specified shape. More particularly, this invention relates to such device and method by taking an image of a target surface by illuminating it from a specified direction and processing an image by regularly reflected light in the generated image.
As a method of defecting surface unevenness of a target object, it has been known to set a camera at a position where regularly reflected light from the target surface can be made incident while this target object is being illuminated from a specified direction. Japanese Patent 2923808, for example, describes a method of detecting the surface unevenness of a glass substrate having a flat surface and Japanese Patent Publication Tokkai 2003-75363 describes a method of detecting defects on the peripheral surface of a cylindrical photosensitive body for electron photography.
If the target surface is of a certain size, it is not possible of obtain the image of the entire surface at once. In such a situation, the camera and the device for the illumination must be moved with respect to the target object. Aforementioned Japanese Patent 2923808 describes the use of an XY moving mechanism for moving the target object parallel to the target surface of inspection and partitioning the target surface into a plurality of areas. Aforementioned Japanese Patent Publication Tokkai 2003-75363 describes the method of rotating the target object around its longitudinal axis to obtain its images.
In recent years, however, fashionable products such as portable telephones and portable music players are frequently designed by combining free-shaped surfaces with different curvatures. Surface conditions of such products, too, are required to be inspected after their production or before their shipment. In order to improve their product value, makers are coming to demand an inspection of a high level. It is extremely difficult, however, to carry out an inspection of the kind using regularly reflected light over the entire surface of a product with portions having different radii of curvature.